The invention relates generally to filters, and more particularly to filters made for applications where industrial coatings are applied.
Paint, and other industrial coatings, are commonly applied to products in manufacturing facilities by spraying the products after placing the products in booths or stations that are separated from the rest of the manufacturing facility. Paint (which is a term used herein to include all industrial coatings) spraying creates “overspray” of atomized particles that do not adhere to the product's surface. Such particles are of various sizes, and can remain wet for some time. Therefore, paint arrestors are used to filter the air inside the paint booth prior to exhausting the air to the environment outside the paint booth to remove wet and dry overspray particles.
Air filtration devices used in booths where painting by spraying is carried out are well known, such as in U.S. Pat. Nos. 3,075,337; 4,008,060; 4,894,073; 5,051,118; and 6,790,397. In these patents, which are incorporated herein by reference, methods and apparatuses are disclosed describing how to take the dry and/or wet particles in suspension out of a gaseous flow, generally air.
To purify such gaseous flows an “inertia” filter can be used. An inertia filter causes turbulence in the flow of gas that contains the paint particles, thereby projecting the suspended particles against the walls of the filters due to the particles' inability to flow around the walls of the filters as well as air. These filters are known in the industry to be sold by Andreae Team, Inc. of Ardmore, Okla. In inertia filters, the filters are of the pleated or accordion type and have two or three walls made of air-impervious material, generally paperboard. These walls are connected along one or two folds and have different dimensions so that chambers are created between the walls. These walls have openings that are not aligned with each other along the direction of air flow. Thus, a turbulent flow of the gas is created within the chambers of the filter. This turbulent flow causes projection of the paint particles, by the inertia of the particles, against the walls of the chambers where they are deposited. Inertia filters ensure a constant pressure drop over their lifetime but have the drawback that they do not retain small, light particles, the mass of which is insufficient for inertia to project them against the walls for deposition. For certain types of paint, particularly lacquers, these filters have an efficiency that cannot satisfy the more strict environmental standards.
Alternatively, filtration can be accomplished by screening/sieving, i.e. by passage of the gas and entrained particles through a porous media with tortuous paths causing impact of the particles with the media, and causing particles to be held when the particles encounter a tortuous path smaller than the particle. These filters typically do not retain dry particles having a size smaller than their pores. Thus, screening filters commonly have a low efficiency. It is possible to make such filters with smaller pores to increase efficiency, but this introduces a substantial pressure drop across the media. Loading with particulate causes such screening filters to clog rapidly, thereby causing an increasing pressure drop, necessitating frequent replacement.
The filters now in use in this field have to be changed often, because government environmental standards generally require arrestance efficiencies greater than or equal to 98%. These filters are made by removable elements intended to be mounted in adapted frames, such as channels into which planar filter cartridges are inserted. The air flow is driven perpendicularly through the filter cartridges as in a residential heating, cooling and ventilation filtration system.
There is a need for an improved filter that has low pressure drop and high paint retention efficiencies, and that does not have to be replaced at a rate that either slows work substantially or causes the cost of use to be too high.